1. Field of the Invention
The present invention relates to a yellow ink composition for ink-jet printing, capable of producing images with excellent color tone and high density, free from image blurring, and also with excellent water resistance, light-resistance, preservation stability, ink ejection stability and drying characteristics. The present invention also relates to a method of recording images by use of such a yellow ink composition.
2. Discussion of Background
Generally, an aqueous ink composition for use in ink-jet printing comprises as constituent components a dye, a wetting agent and water.
As the dyes for use in such aqueous ink compositions, there are known acid dyes, direct dyes and basic dyes. However, of such dyes, basic dyes are not used so much in an aqueous ink composition for ink-jet printing. Instead, direct dyes or acid dyes are primarily employed in view of sufficient safety and preservation stability thereof for use in practice.
In conventional inks for ink-jet printing, as direct dyes, for example, C.I. Direct Yellow 1, 8, 12, 24, 26, 33, 44, 50, 86, 120, 132 and 144 are employed; and as acid dyes, for example, C.I. Acid Yellow 17, 42, 44, 79 and 142 are employed.
However, when an ink composition containing such a direct dye is used in ink Jet printing, there are caused various problems which stem from poor preservation and ejection stabilities of the ink composition.
More specifically, precipitates are formed in the ink composition or the physical properties of the ink compositions change during an extended period of storage, or while in continuous use or not in use in an ink-jet printing apparatus, an the nozzles of the ink jet printing apparatus are clogged with the ink composition during the periods of use and non-use thereof, because of the poor solubility of the direct dye in the ink composition.
Many acid-dye-containing ink compositions are capable of yielding excellent color tone, but images formed or recorded by acid-dye containing ink compositions have poor water resistance and light-resistance and therefore lack preservability.
For example, Japanese Laid-Open Patent Application 2-233781 discloses an ink composition which employs a direct dye, C.I. Direct Yellow 86, for ink jet printing, attempting to improve the color reproduction performance thereof. However, the preservation stability and ejection stability of the ink composition are insufficient and lacks reliability for use in practice.
A dye of the following general formula, including a counter ion, --NH.sub.4 represented by M, which is intended to improve the water resistance thereof, was proposed by R. W. Kenyon of ZENECA Co., Ltd. at the 9th International Congress on Advances in Non-Impact Printing technologies/JAPAN HARDCOPY '93: ##STR4##
When an ink composition containing the above dye is employed for ink jet printing, images with excellent color tone and water resistance can be produced, but the image density thereof is low, and the preservation stability and ink ejection stability of the ink composition are insufficient for use in practice and therefore the ink composition lacks operational reliability.
In order to obtain recorded images with high image density, it is necessary to increase the concentration of a dye in an ink composition for ink jet printing. In order to increase the concentration of a dye in an ink composition, it is necessary that the solubility of the dye in the ink composition be high.
The solubility of the dye in the ink composition has significant effects on the preservation stability and ejection stability of the ink composition.
Dyes used in conventional ink compositions for ink jet printing do not have high solubility and dissolving stability, and therefore such conventional ink compositions are not capable of recording images with high density, excellent color tone, high water resistance and light-resistance, and do no have excellent preservation stability and ejection stability.
Furthermore, surfactants are added to conventional ink compositions for ink jet printing in order to improve the drying rate of images printed by the ink compositions. Such surfactants have the functions of decreasing the surface tension of the ink compositions and therefore increasing the penetration of the ink compositions into image receiving paper, thereby increasing the drying rate of the printed images.
Japanese Laid-Open Potent Application 55-29546 discloses an ink composition which comprises a surfactant. In this ink composition, by use of a surfactant, the penetration of the ink composition into paper is increased, thereby increasing the drying rate of images printed on paper. However, this ink composition has the shortcoming that printed images considerably spread on some paper so that image quality is significantly lowered.
Japanese Patent Publication 80-23793 discloses an ink composition which comprises a dialkylsulfosuccinate as a surfactant for improving the drying rate of printed images and minimizing the deterioration of printed images. However, when sodium dioctylsulfo-succinate or sodium dihexylsulfosuccinate is used as the surfactant, the diameters of picture elements of printed images vary on some paper, and when the pH of the ink composition is on an alkaline side, such a surfactant may be decomposed, and therefore the effect of such a surfactant will be lost when preserved for an extended period of time.
Japanese Laid-Open Patent Application 56-57862 discloses an ink composition comprising a strong basic material for improving the drying rate of printed images. Such an ink composition is effective for the improvement of the penetration of the ink into a rosin-sized acidic paper, but not effective for a paper sized with an alkyl ketene dimer or alkenyl sulfosuccinic acid.
Furthermore, even in the case of the acidic paper, the above-mentioned ink composition is not effective for a two-color-superimposed portion thereof.
Japanese Laid-Open Patent Application 1-203483 discloses an ink composition comprising a polyhydric alcohol derivative and pectin in an attempt to increase the drying rate of the ink composition and to prevent the blurring of the ink composition on paper, thereby obtaining recording images with excellent image quality. However, when this ink composition is used in an ink-jet printer, the ejection of the ink composition from the nozzles of the printer is unstable when the printing operation is resumed after some intermission, because pectin is a nonionic material having hydroxyl groups as hydrophilic groups and has poor water solubility.
Thus, it is extremely difficult to improve the drying rate of printed images, without impairing the ejection stability, while preventing the blurring of printed images and obtaining recorded images with excellent image quality, by conventional ink compositions for ink jet printing.
In order to perform excellent ink jet printing over a long period of time, it is required that an ink composition for ink-jet printing satisfy the following conditions:
(1) The viscosity, surface tension, specific electric conductivity and density of the ink composition fall within certain appropriate respective ranges which are suitable for an ink droplet formation method and a method of controlling the direction of ejected ink droplet streams employed. Thus, the ejection characteristics the ink composition are excellent. PA1 (2) The preservation stability of the ink composition is so good that no precipitates are separated or formed, due to chemical changes or other causes, from the ink composition during an extended period of storage, or during the periods when an ink jet printing apparatus is in continuous use, or not in use, and no physical properties of the ink composition change during the above-mentioned periods. PA1 (3) The ejection stability of the ink composition is so good that the direction of the ejected ink droplet streams is not shifted from a predetermined direction and the weight of each ink composition droplet is not changed during continuous ejection for recording by an ink jet printing apparatus, or when ink jet printing is resumed after a non-use period, and that the nozzles of the ink jet printing apparatus are not plugged with the ink composition. PA1 (4) Images printed by the ink composition have excellent color tone and sufficiently high density and are clear and free from blurring. PA1 (5) Images printed by the ink composition dry rapidly. PA1 (6) Images printed by the ink composition are sufficiently resistant to water, light and physical wear for use in practice. PA1 a water-soluble dye which comprises (a) a dye compound of formula (I), ##STR5## wherein X and Y are each selected from the group consisting of a hydrogen atom, an alkyl group, an alkoxyl group and a halogen; Z is an alkanolamine group; M.sup.+ is selected from the group consisting of an alkali metal cation, a quaternary ammonium cation, a quaternary phosphonium cation, and an alkanol amine cation; and j and k are each an integer of 0 to 3, and (b) at least one of a dye compound of formula (II) ##STR6## wherein Z and M.sup.+ are respectively the same; and l and m are each an integer of 0 to 3, or a dye compound of formula (III) ##STR7## wherein X, Y and M.sup.+ are respectively the same as in formula (I), a surfactant, and PA1 a wetting agent. PA1 a water-soluble dye which comprises (a) a dye compound of formula (I), ##STR14## wherein X and Y are each selected from the group consisting of a hydrogen atom, an alkyl group, an alkoxyl group and a halogen; Z is an alkanolamine group; M.sup.+ is selected from the group consisting of an alkali metal cation, a quaternary ammonium cation, a quaternary phosphonium cation, and an alkanolamine cation; and j and k are each an integer of 0 to 3, and (b) at least one of a dye compound of formula (II) ##STR15## wherein Z and M.sup.+ are respectively the same; and l and m are each an integer of 0 to 3, or a dye compound of formula (III), ##STR16## wherein X, Y and M.sup.+ are respectively the same as in formula (I), a surfactant, and PA1 a wetting agent.
However, conventionally it is difficult to obtain an ink composition for ink jet printing, particularly, a yellow ink composition for ink jet printing, which is capable of producing recorded images with excellent color tone, water resistance, and light-resistance, and with high image density, and improved drying rate, free from blurring, and which has excellent preservation stability and ejection stability.